Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Thus, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. During planarization, the substrate is typically mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push the substrate against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The effectiveness of a CMP process may be measured by the CMP process's polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
The CMP retaining ring functions to retain the substrate during polish. The CMP retaining ring also allows slurry transport under the substrate and affects edge performance for uniformity. However, typical CMP retaining rings have no integrated sensors that can be used for closed loop control during process, diagnostics or providing feedback on the endpoint of chemical-mechanical polishing processes and catastrophic events, such as for example, substrate breakage or slip out.
Therefore, the inventor believes that structures and methods that accomplish accurate and reliable detection of the endpoint of chemical-mechanical polishing processes and catastrophic events are desirable.